◆3 8..8888。 T23 02 FIGURE 2.1 Definitions of principal material directions for an orthotropic lamina and stress components. E1 Su S12 0 E2 S12 0 62 (2.4 Y12 0 0 The compliance elements Si may be related to the engineering constants (E1,E2,G12V12V2 S11=1/E1,S2=-V12/E1=-V2:/E2 (2.5a) S2=1/E2,S6=1/G12 (2.5b) The engineering constants are average properties of the composite ply.The quantities E and vi2 are the Young's modulus and Poisson's ratio,respectively, corresponding to stress o1(Figure 2.2a) E1=o1/e1 (2.6a) V12=-e2/e (2.6b) E2 and v2 correspond to stress 02(Figure 2.2b) E2=o2/e2 (2.7a V21=-e1/e2 (2.7b) For a unidirectional composite E2 is much less than E,and va is much less than v12.For a balanced fabric composite E=E2 and vi2=V2.The Poisson's ratios vz and vz are not independent ©2003 by CRC Press LLC(2.4) The compliance elements Sij may be related to the engineering constants (E1, E2, G12, ν12, ν21), S11 = 1/E1, S12 = –ν12/E1 = –ν21/E2 (2.5a) S22 = 1/E2, S66 = 1/G12 (2.5b) The engineering constants are average properties of the composite ply. The quantities E1 and ν12 are the Young’s modulus and Poisson’s ratio, respectively, corresponding to stress σ1 (Figure 2.2a) E1 = σ1/ε1 (2.6a) ν12 = –ε2/ε1 (2.6b) E2 and ν21 correspond to stress σ2 (Figure 2.2b) E2 = σ2/ε2 (2.7a) ν21 = –ε1/ε2 (2.7b) For a unidirectional composite E2 is much less than E1, and ν21 is much less than ν12. For a balanced fabric composite E1 ≈ E2 and ν12 ≈ ν21. The Poisson’s ratios ν12 and ν21 are not independent FIGURE 2.1 Definitions of principal material directions for an orthotropic lamina and stress components. 1 2 12 11 12 12 22 66 S S S S S ε ε γ σ σ τ             =                         0 0 0 0 1 2 12 TX001_ch02_Frame Page 12 Saturday, September 21, 2002 4:48 AM © 2003 by CRC Press LLC